Several different types of equipment are used for size reduction or comminution of materials to fine particles or powder. Crushing rolls, rock crushers, hammer mills and ball mills are examples of such equipment, and are generically referred to herein as “comminution apparatus”. The decision to select a particular type of comminution apparatus depends, at least in part, on the size distribution desired for the resulting product and on the properties of the feed material. Crushing rolls, for example, may be particularly suitable for coarse size reduction of brittle materials and for materials that fracture under pressure without smearing or flowing.
Certain materials, such as light metals, including zirconium, titanium and niobium, for example, cannot be effectively reduced (i.e., comminuted) to fine powder using crushers because these metals have a tendency to gall, and chips of the metals would stick to the cutting edges. To address this problem, such metals have first been subjected to hydrogen embrittlement and then reduced in, for example, a ball mill. Hydrogen is later removed from the reduced material in a vacuum furnace to produce a suitable metal or metal alloy powder. This process is expensive and may still produce powder containing unacceptably high levels of hydrogen and oxygen.